(1) FIELD OF THE INVENTION
The present invention relates to a system and method for controlling engine output to suppress wheel slip which are applicable to an automotive vehicle.
According to the present invention, the engine output controlling system includes, in addition to a first throttle valve linked with an acceleration element, a second throttle valve which is externally controllable. Engine output is controlled by actuating to open and close the second throttle valve to suppress slips occurring on drive wheels.
(2) BACKGROUND ART
Japanese patent application First Publication (Unexamined) No. Showa 62-45944 published on Feb. 7, 1987 exemplifies a previously proposed system for controlling engine output to suppress drive wheel slippage.
In the previously proposed system, another (second) throttle valve which is externally controllable is installed within a throttle chamber of an intake air passage of a vehicular engine in series with the usual (first) throttle valve which is linked to the accelerator pedal.
During occurrence of slippage affecting drive wheels, the second throttle valve is controlled in three modes, i.e., fully open, hold, and fully closed, according to situations (,e.g., magnitude) in which drive wheel slippage occurs. Then, a control system for the second throttle valve, independent of the acceleration system including the first throttle valve, controls an opening angle of the second throttle valve to reduce engine output (torque) so as to suppress drive wheel slippage.
In addition, when the engine output reduction control condition is not satisfied, i.e., the engine output is not controlled, the opening angle of the second throttle valve is made in accordance with that of the first throttle valve, i.e., is controlled so as to follow-up the opening angle of the first throttle valve, i.e., 1:1.
Therefore, in a case where engine output reduction control is not carried out for a longer period of time or for a longer duration of time, a sticking of the second throttle valve due to a clogging of fuel in the throttle chamber or adhering foreign matters or so on thereon can be prevented.
On the other hand, since the engine output reduction control is resumed a short period of time after the end of the engine output reduction control, the second throttle valve can be returned in a very short period of time toward a predetermined narrow opening angle and responsive characteristic of reducing a slip rate of drive wheels can be improved.
However, the previously proposed system described above has the following problems since the opening angle of the second throttle valve always follows up that of first throttle valve.
(1) an actuator installed for opening and closing the second throttle valve has lesss durability.
(2) the second throttle valve arranged in the intake passage in series with the first throttle valve provides an intake air resistance for the engine intake air and a turbulence of the engine intake air is produced.
It is noted that if the second throttle valve provides intake air resistance for the engine intake air and the turbulence is generated in the intake air, the engine output corresponding to an accelerator operating variable does not appear. In addition, The follow-up control of the second throttle valve has an ill effect such as to delay the engine output responsive characteristic for a change in the operation of accelerator. For example, in a case where a bypass intake air passage for EGR is installed upstream of the second throttle valve, an excessive lack in a flow quantity through the bypass intake air passage for EGR is generated.